Polar Stratospheric Clouds (PSCs)
qIn winter the polar stratosphere is so cold (-80°C or below) that certain trace atmospheric constituents can condense.
qThese clouds are called “polar stratospheric clouds” (PSCs).
qThe particles that form typically consist of a mixture of water and nitric acid (HNO3).
qThe PSCs alter the chemistry of the lower stratosphere in two ways:
q (1) by coupling between the odd nitrogen and chlorine cycles
q (2) by providing surfaces on which heterogeneous reactions can occur.
(Sweden,
January 2000; from NASA website)